Dusk Watchman (Twilight Reign, Book 5)

There is one final, desperate chance for victory: a weapon, so terrible only a dead man could wield it, and only a madman would try. But if they do not grasp this opportunity, King Emin and his allies will be obliterated as Ruhen's millennia-old plans are about to bear terrible fruit. If his power continues unchecked, Ruhen will achieve total dominion - and not just over mankind, but over the Gods themselves.
One way or another, the future of the Land will be decided now - written in the blood of men.

Long Synopsis:

After his pyrrhic victory at Moorview, King Emin learns the truth about the child Ruhen - but he is powerless to act. Instead, he must mourn his dead friends while his enemy promises the beleaguered peoples of the Land a new age of peace. The past year has taken a grave toll: the remaining Menin troops seek revenge upon Emin, daemons freely walk the Land, and Ruhen's power is increasing daily.
And yet, a glimmer of hope remains. There is one final, desperate chance for victory: a weapon, so terrible only a dead man could wield it, and only a madman would try. But if they do not grasp this opportunity, King Emin and his allies will be obliterated as Ruhen's millennia-old plans are about to bear terrible fruit. If his power continues unchecked, Ruhen will achieve total dominion - and not just over mankind, but over the Gods themselves.
One way or another, the future of the Land will be decided now - written in the blood of men.